The present invention relates to coatings on polymer substrates. More specifically, the present invention relates to thin coatings on polymer substrates that are applied with low energy, and methods of coating polymer substrates.
A multitude of thin coating techniques have been disclosed in the prior art, including sputter coating, physical vapor deposition, melt extrusion, solvent deposition and high energy buffing. These techniques have disadvantages in requiring highly specialized equipment or involving the evaporation of volatile organic solvents (VOC""s) that may be a source of pollution. Alternatively, these techniques may require the input of large amounts of energy. Further, many of these techniques do not provide a satisfactorily thin and uniform coating, and may change the morphology of the material to be coated in an unsatisfactory manner.
U.S. Pat. No. 4,741,918 to de Nagybaczon, et al. discloses a coating process wherein dry particles are coated on a substrate with a high-energy buffing wheel. Because a buffing wheel is used, this process inherently orients the particles in the direction of travel of the buffing wheel on the substrate. The coating of this disclosure is described as having a characteristic xe2x80x9csmeared appearancexe2x80x9d at column 3, lines 49-50.
In the prior art on high energy buffing all previous methods disclose only a rotary motion of an applicator pad with the rotational axis parallel to the plane of the substrate or the web.
A method of coating a polymer substrate with a dry composition comprising particles is provided. The particles have a Mohs"" hardness between 1 and 2.5 and a largest dimension of less than 100 microns. The particles are buffed on the substrate at a pressure of less than about 30 g/cm2 with an applicator which moves in a manner parallel to the surface of the substrate. When the particles have one dimension longer than other dimensions, the particles are randomly oriented in the plane of the substrate. The composition preferably contains no materials in an amount effective to act as a binder.